The input and/or output impedances of integrated circuits typically need to be regulated to achieve a desired performance from the integrated circuits without signal degradation. For example, FIG. 1 is a schematic block diagram illustrating a conventional input impedance biasing circuit according to the prior art. In FIG. 1, a capacitor 102 may represent a portion of a microphone and be coupled to circuitry of an audio controller. A high impedance may be desired at input node 106 of additional circuitry 104. As illustrated in FIG. 1, a conventional system to provide high impedance at input node 106 includes an impedance string 110 that consists of a complementary string of polysilicon diodes connected in anti-series. Depending on the impedance provided by impedance string 110, a start-up switch 112 may be included to initialize the input node 106 to a desired voltage, such as VCMin.
Numerous drawbacks are associated with conventional input impedance biasing circuits, such as impedance string 110. For example, the impedance provided at input node 106 by impedance string 110 may vary significantly across operating temperatures. The variation may make it difficult for audio controller 100 to meet different specifications, such as linearity and signal to noise ratio (SNR).
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved electrical components, particularly for improved input impedance biasing circuits. Embodiments described herein address certain shortcomings but not necessarily each and every one described here or known in the art.